There seem to be two different styles or emphases in serving Hashem:
1) Time-related, i.e., that one gives precedence to an inyan she’hazman gromo (a matter of timely relevance). Indeed, the Rebbe says clearly that generally speaking, an inyan she’hazman gromo takes precedence over other things, e.g., studying this week’s Torah portion, the laws in Shulchan Aruch concerning the soon-approaching Yom-Tov, or studying the explanation of the Rebbeim concerning the significance of an approaching yoma depagra (Chassidishe holiday).
This appears to contain a strong element of kabolas ol (“acceptance of the yoke” of divine sovereignty), because of course we can’t choose whether to enter a particular time of year; the passage of time is not at all in our control.
2) Types of avoda (divine service) that are not time-related. Of this there are two types:
a. Mitzvos that apply constantly, like the Sefer HaChinuch’s six constant Mitzvos, or regularly, like the daily obligations to davven, learn Torah, etc.
b. Working on individual middos until they are fixed, as is recommended in the Rebbe Rashab’s Kuntres HoAvodah. This depends only upon where one is up to in his individual Avodah, and not the calendar. Here there appears to be less kabolas ol involved in the sense that although effort is required, you dedicate yourself to refining the character trait that you choose, to figure out what Hashem wants of you using your own mind. Indeed, divine service requires the regular advice of a mashpia, but that is often more a matter of “eitza toivo ko’mashma lon”—advice that one follows voluntarily and willingly, rather than due to the duress of an unquestionable order from above (cf. Sefer HaSichos, Shoftim, 5751).
In the excerpt below the Rebbe discusses this concept in connection with Tes Kislev (the anniversary of the birthday and Histalkus (passing) of the Mitteler Rebbe and Yud Kislev, the anniversary of the liberation of the Mitteler Rebbe:
There is an obligation to learn the entire Torah throughout the year. Nevertheless, there are certain times in which certain topics in Torah take priority, [and of this it is written that one should study] “the laws of the festival on the festival,” and the like, since this is a matter of timely relevance [“inyan she’hazman gromo”].
Even on the days of Tes and Yud Kislev we are involved with many additional things (aside from matters related to the Mitteler Rebbe)—meaning that only a certain part of the day is dedicated to the matter of timely relevance, and not the entire day. Nevertheless, all things done on this day, even those apparently done the same as throughout the year, are permeated with the matter of timely relevance, since this is the primary aspect of significance in this day.
Hisva’aduyos 5743, Vol. 1, p. 525.